Intermediate Mass Black Holes

Current Research Interests

Stellar mass black holes (MBH = 5-100 M ) form from the collapse of dead stars or the merger of black holes. In the Milky Way, several stellar mass black holes have been detected through X-ray observations or gravitational wave signatures. At the high mass end, all massive galaxies like the Milky Way contain supermassive black holes (SMBHs) at their centers with MBH 106 M . However, between the two extreme mass ranges, intermediate mass black holes (IMBHs) remain relatively scarce. IMBHs create a clearer picture of black hole evolution as they represent a transitional state between stellar mass black holes and SMBHs. Similarly, evidence suggests that SMBHs and their host galaxies co-evolve with one another, and so finding IMBHs also deepens our knowledge of galaxy evolution.

While all massive galaxies contain SMBHs, it stands to reason that a significant fraction of dwarf galaxies should contain IMBHs. Finding actively accreting IMBHs, or AGN, in dwarf galaxies helps determine a lower limit on the frequency of IMBHs at z ~ 0. Determining the frequency of dwarf AGN in the local universe is an open area of research that our group is currently pursuing. The photoionization simulations our group runs provides the spectroscopic and photometric signatures needed to identify dwarf AGN. Specifically, I'm interested in improving photoionization models through deepening our understanding of the low mass AGN SED, degenercies with HMXBs, and complex cloud geometries.

Recent Publications

  • Polimera, M. S., Kannappan, S. J., Richardson, C. T., Bittner, A. S., Ferguson, C., "Finding Low-Metallicity z~0 Dwarf AGN Candidates in the RESOLVE and ECO Surveys using Optimized Emission Line Diagnostics", 2022, ApJ, 931, 44
  • Richardson, C. T., Simpson, C., Polimera, M. S., Kannappan, S. J., Bellovary, J. M., Greene, C., Jenkins, S., "Optical and JWST Mid-IR Emission Line Diagnostics for Simultaneous IMBH and Stellar Excitation in z ∼ 0 Dwarf Galaxies", 2022, ApJ, 927, 165
  • Richardson, C. T., Allen, J. T., Baldwin, J. A., Hewitt, P. C., Ferland, G. J., "Interpreting the Ionization Sequence in AGN Emission-Line Spectra", 2014, MNRAS, 437, 2376
  • Allen, J. T., Hewitt, P. C., Richardson, C.T., Ferland, G. J., Baldwin, J. A., "Classification and Analysis of Emission Line Galaxies Using Mean Field Independent Component Analysis", 2013, MNRAS, 430, 3510